A known lane-change warning system disclosed in JP1997-132094A (hereinafter referred to as Patent document 1) is configured so as to detect operation of a turn signal, which is conducted when a driver moves a turn signal operating lever for activating a turn signal light. When the operation of the turn signal is detected, an obstacle detection device for detecting an obstacle located in a lateral and rearward area around a vehicle of the driver detects an obstacle existing in a rearward area around the vehicle. The lane-change warning system warns the driver about the obstacle in accordance with a result of the detection of the obstacle detection device. In the lane-change warning system, an obstacle, which is located in the lateral and rearward areas of the vehicle in the next lane on which the driver is driving, is detected. When a distance between the vehicle and the laterally rearward obstacle is a predetermined distance or longer and when a relative speed therebetween is higher than a predetermined speed, the lane-change warning system controls the turn signal operating lever to be returned to a neutral position right after the driver moves the turn signal operating lever. Meanwhile, when a relative distance between the vehicle and the laterally rearward obstacle is shorter than the predetermined distance, the lane-change warning system controls the turn signal operating lever not to be easily moved without a predetermined degree of force. With the technique described in Patent document 1, since a warning about a risk of the obstacle approaching the vehicle is issued by means of the turn signal operating lever, the driver may easily recognize the warning. Moreover, the driver is less likely to feel confused, compared to a case where the driver is warned about a risk of an obstacle approaching the vehicle by means of a sound. In addition, the driver is prevented from not recognizing the warning. Accordingly, the risk is surely notified to the driver.
Further, a known turn signal sound generating system for a vehicle, which generates different turn signal sounds in accordance with an operating condition of a turn signal of the vehicle and in accordance with a speed of the vehicle, is disclosed in JP2000-272414A (hereinafter referred to as Patent document 2). In a condition where the turn signal is in operation and in a condition where the speed of the vehicle is higher than a predetermined speed, changing lanes is determined to be dangerous based on information from side and rear monitors, which monitor other vehicles moving from lateral and rearward directions of the vehicle. At this time, the turn signal sound generating system operates a turn signal generator to emit a warning sound. With such technique, a speed of the vehicle at which a turn signal sound switches is linked to a speed of the vehicle at which the side and rear monitors start operating. Accordingly, a driver of the vehicle may recognize whether or not the side and rear monitors are in operation, by hearing and distinguishing different turn signal sounds. Consequently, the driver surely focuses on a warning sound indicating a risk of other vehicles approaching the vehicle of the driver when he/she changes lanes.
Furthermore, a side-rear monitoring system for a vehicle, disclosed in JP3464368B2 (hereinafter referred to as Patent document 3) detects another vehicle approaching from a rearward direction of the vehicle of a driver or from the next lane of a lane on which the driver is driving, on the basis of an image of a scene located in lateral and rearward areas of the vehicle of the driver. The side-rear monitoring system detects another vehicle approaching the vehicle of the driver by means of an image signal obtained by an imaging device, thereby determining a risk level of the approach of another vehicle and a direction in which the risk level is high, depending on how close the two vehicles are located to each other. The side-rear monitoring system includes a first warning indicator arranged near a right side mirror, a second warning indicator arranged near a left side mirror, and a third warning indicator arranged near a rear view mirror. When a risk of the approach of another vehicle from the right adjoining lane to the driving lane on which the vehicle of the drive is moving is high, a warning about the risk is indicated by the first warning indicator. When a risk of approach of another vehicle from the left adjoining lane to the driving lane is high, a warning about the risk is indicated by the second warning indicator. When a warning about another vehicle approaching the vehicle of the driver from the rearward direction is high, a warning about the risk is indicated by the third warning indicator. According to the technique described in Patent document 3, the warning about the approach of another vehicle is issued to the driver with one of the related warning indicators corresponding to the direction in which the risk exists. Accordingly, the driver easily recognizes the direction in which the risk exists. Moreover, when the driver looks at one of the related warning indicators, he/she instinctively looks at the side mirror. Thus, the side-rear monitoring system enables the driver to instinctively focus on another vehicle approaching his/her vehicle.
A turn signal serves to notify an intention of a driver to turn right or left or to change lanes to other drivers driving around a vehicle of the driver. For example, it is appropriate for the driver to change lanes after confirming that no vehicle is approaching from lateral and rearward directions of his/her vehicle, operating a turn signal operating lever, and notifying his/her intention to change lanes to the drivers around him/her. Thus, the driver's intention to change lanes is generally determined by the operation of the turn signal operating lever.
According to the techniques of Patent document 1 and Patent document 2, a warning about an existence of an obstacle around the vehicle is issued after the driver operates the turn signal operating lever, i.e., the driver in a condition where his/her intention to change lanes is fixed and he/she is ready to change lanes. Accordingly, even though the warning is issued, the driver may not prevent a collision between the vehicle and the obstacle. Consequently, the warning should be issued not after the driver operates the turn signal operating lever and his/her intention to change lanes is fixed but before the driver operates the turn signal operating lever with a decision to change lanes.
In addition, according to the techniques described in Patent documents 1 to 3, the warning may be issued even when the driver does not need the warning. In particular, according to the technique of Patent document 3, the side-rear monitoring system issues the warning even when the driver is in a normal driving condition without having his/her intention to change lanes, therefore issuing an ambiguous or confusing warning to the driver. Although a switch for indicating and not indicating the warning may be optionally applied to the side-rear monitoring system, turning the switch on/off when needed is troublesome for the driver. Such changing operation of the switch is not appropriate for the driver to drive safely.
A need thus exists for a vehicle surrounding recognition support system for a vehicle, which is not susceptible to the drawbacks mentioned above.